ssl: Don't ignore non-ragged EOF
Testing NEO/go client wrt NEO/py server revealed a bug in NEO/py SSL handling: proper non-ragged EOF from a peer is ignored, and so leads to hang in infinite loop inside _SSL.receive with read_buf memory growing indefinitely. Details are below:
NEO/py wraps raw sockets with
ssl.wrap_socket(suppress_ragged_eofs=False)which instructs SSL layer to convert unexpected EOF when receiving a TLS record into SSLEOFError exception. However when remote peer properly closes its side of the connection, socket.read() still returns b'' to report non-ragged regular EOF:
https://github.com/python/cpython/blob/v2.7.18/Lib/ssl.py#L630-L650
The code was handling SSLEOFError but not b'' return from socket recv.
Thus after NEO/go client was disconnecting and properly closing its side
of the connection, the code started to loop indefinitely in _SSL.receive
under while 1 with b'' returned by self.socket.recv() appended to
read_buf again and again.
-> Fix it by detecting non-ragged EOF as well and, similarly to how SSLEOFError is handled, converting them into self._error('recv', None).